Systematic review and meta-analysis of hydrocarbon exposure and the risk of Parkinson's disease

BACKGROUND: There is no consensus on the association between exposure to hydrocarbons and the risk of Parkinson's disease (PD). We conducted a systematic review and meta-analysis to summarise the epidemiological evidence and included a new large case-control study.

METHODS: Data were extracted following a predefined protocol. Risk estimates regarding the association between hydrocarbon exposure and PD were consolidated to produce a summary odds ratio (OR), 95% confidence intervals (CI), and p-value. In our case-control study, 1463 PD patients and 685 controls were recruited from clinical trials and completed a structured questionnaire describing their previous working exposure to hydrocarbons and other demographic measures. The association between exposure to hydrocarbons and risk of PD was evaluated using logistic regression.

RESULTS: The systematic search identified 13 case-control studies matching the inclusion criteria. The meta-analysis included 3020 PD cases and 6494 controls. The summary OR was 1.32 (95% CI 1.08-1.62, p = 0.006) for hydrocarbon exposure (ever versus never). In the PD GEN study, occupational exposure to hydrocarbons significantly increased the risk of PD (OR = 1.61; 95% CI 1.10-2.36, p = 0.014), and risk dose-dependently increased for subjects exposed greater than 10 years compared to subjects never exposed (OR = 2.19; 95% CI 1.13-4.26, p = 0.021). The addition of PD GEN data increased the total numbers to 4483 PD cases and 7179 controls and strengthened the significant association (summary OR = 1.36; 95% CI 1.13-1.63, p = 0.001).

CONCLUSIONS: This systematic review supports a positive association between hydrocarbon exposure and PD. Data from prospective studies are required to reinforce the relationship between hydrocarbon exposure and PD.